This invention relates generally to epitaxial growth in semiconductor fabrication processes and, more particularly, to the fabrication of thick films, greater than approximately 50 microns (50 .mu.m) thick. Probably the most significant problem in very thick film growth is stress-induced breakage of semiconductor wafers being processed. It is with this problem that the present invention is concerned.
In epitaxial processing, layers of various materials, usually silicon-based, are grown by a deposition process in a processing chamber. Typically, semiconductor silicon wafers are first loaded onto the outer surfaces of a silicon carbide coated graphite support, called a susceptor. The susceptor has multiple flat external surfaces to accommodate a number of large wafers, and the entire susceptor is lowered into a quartz processing jar, into which appropriate gases are admitted to effect formation of a layer of material on the silicon wafers. To ensure uniformity of deposition of the film, the susceptor is rotated at a uniform speed, about its vertical axis. Without the rotation, the thickness profile would tend to vary depending on a number of factors, such as the relative location of processing gas inlet ports.
After an appropriate time, the susceptor rotation is stopped, the susceptor and wafers are cooled down, the susceptor is lifted from the quartz jar, and the wafers are removed from the susceptor. For films in excess of 50 microns (50 .mu.m), cooldown often results in bending and breakage, sometimes referred to as microcracking, of some of the wafers. Prior to this invention, there has been no effective technique for minimizing or eliminating this wafer damage problem.